Merten



April 17, 1962 E. MERTEN Re. 25,160

PHOTOGRAPHIC PRINTING APPARATUS FOR SEISMIC AND OTHER RECORDS OriginalFiled Sept. 30. 1952 5 Sheets-Sheet 1 5 LINE 3!. 450 NOA N I 2 3 4 5 6Fig. I

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April 17, I962 SEISMIC AND OTHER RECORDS Original Filed Sept 30. 1952 5Sheets-She et 2 Puma Z. IknmO ooom ooom 00o.

Apnl 17, 1962 E. MERTEN Re. 25,160

PHOTOGRAPHIC PRINTING APPARATUS FOR SEISMIC AND OTHER RECORDS OriginalFiled Sept. :50. 1952 5 Sheets-Sheet 5 LINE 31 450 "0A Sign Fig. 5

is A kn-neg April 17, 1962 E. MERTEN Re. 25,160

PHOTOGRAPHIC PRINTING APPARATUS FOR SEISMIC AND 02mm RECORDS OriginalFiled Sept. 30. 1952 5 Sheets- Sheet 4 s uni In 450 Mon N I 2 3 4 5 6lnven+or His AHorneg Fig.6

April 17, 1962 E. MERTEN Re. 25,160

PHOTOGRAPHIC PRINTING APPARATUS FOR SEISMIC AND 0mm RECORDS OriginalFiled Sept. 30. 1952 5 Sheets-Sheet 5 B 1 o co i I 6 w m I: m m

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Eugen Mari-en His lHor-neg United States Patent Ofilice Re. 25,160Reissued Apr. 17, 1962 25160 PHOTOGRAPHIC PRIN TIN G APPARATUS FORSEISMIC AND OTHER RECORDS Eugen Merten, Houston, Tex., assignor toShelli Development Company, Emeryville, Califi, a corporation ofDelaware.

Original No. 2,821,892, dated Feb. 4, 1958, Ser. No. 312,266, Sept. 30,1952. Application for reissue Feb. 16, 1959, Ser. No. 793,653

5 Claims. (Cl. 95-73) Matter enclosed in heavy brackets [I appears inthe original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

This invention pertains primarily to. seismic. exploration, and relatesto an improved type of exploratory seismic records or seismograms, andto a method and apparatus for forming such records.

It is, however, understood that said method and apparatus are notlimited to the production or reproduction of seismic records only, butmay be used in forming or reproducing photographic and other records ofany type, especially when it is desired to change said records to adifferent or variable scale, as will appear hereinbelow. For purposes ofclearness, however, and because of the fact that the present method andapparatus find a particularly advantageous application in seismic work,said method and apparatus will be described and illustrated with regardto their use in producing seismic records.

Depending on the recording method used, seismograms obtained in seismicWork may be of the variable amplitude or variable area type, wherein therecord is produced in the form of an oscillatory line whose amplitude ofoscillations or squiggles is proportional to the intensity of theelectric impulses, or of the variable density type, in which the recordis produced in the form of a track wherein the densityof the light imageis proportional to the intensity of said impulses.

Neither the variable amplitude nor the variable density records,however, even when obtained in accordance with a method of explorationsuch, for example, as the continuous profiling method, and subsequentlyproperly arranged and grouped, are capable of giving a sufficientlyclear picture permitting an observer to visualize by inspection theunderground conditions of the area under survey.

It is a general object of this invention to provide a method andapparatus whereby a record of any type may be reproduced to a differentscale susceptible to make said record easier for reading, interpretationor correlation purposes.

It is also an object of this invention to provide a method and apparatuswhereby a record may be reproduced to any desired size, the scale atwhich the reproduction is effected being varied during the very processof reproduction, as will appear hereinbelow.

It is a particular'object of this invention to provide, as a visual aidin seismic exploration, an improved type of seismic record adapted tosimplify seismic interpretation and correlation, anda method andapparatus for producing such records.

It is also an object of this invention to provide a method and anapparatus. by means of which variable amplitude, variable area orvariable density type seismic records made directly in the field, orobtained in the laboratory from such field records, can be grouped,modified and displayed so as to give a clear composite visual picture ofthe nature and arrangement of underground strata.

It is also an object of this invention to provide a method and anapparatus whereby said composite seismic picture. is automaticallyreduced at the time of the formation 2 thereof to a suitable andconsistent horizontal scale, is: given a proper weathering correction,and is automatically changed from a, vertical reflection-timescale to acorrect vertical distance scale, thereby minimizing chances of error onrecord inspection.

These and other objects of this invention will be understood from thefollowing description taken with reference to the attached drawings,wherein:

FIG. 1 shows the initial stage of a composite Seismogram of the presentinvention;

FIG. 2 is a, diagrammatic plan view of an embodiment of the apparatus ofthe present invention;

FIGS. 3 and 4 show intermediate stages of a composite. seismogram of thepresent invention;

FIG. 5 is a diagrammatic representation of a time-depth graph used incorrecting the vertical scale of the present seismograms;

FIG. .6 shows the final stage of a composite seismogram of the presentinvention;

FIG. 7 is a plan view of another embodiment of the present invention.

As well known to those familiar with seismic surveying and as moreparticularly described in my co-pending application Serial No. 217,541,filed March, 26, 1951,, now Patent No, 2,710,070, issued June 7, 1955,conventional seismic profiling work is carried out by disposing, along apreferably straight line and in contact with the ground, a spread of aplurality of. seismometcrsv or detectors, of which one-half maybelocated to one side of theshot' point, and the other half to the otherside thereof, the total distance occupied bythe spread being of theorder of from 1000 to 4000 feet.

A, recording unit is. electrically connected to the detectors to amplifyand record in well-known fashion the electrical impulses produced by thedetectors upon the arrival thereto of seismic waves generated by theexplosion at the shot point and reflected or refracted by the variousunderground formations.

After an explosion has been recorded, the detectors and the recordingunit are moved further along the original profiling line and anothershot is exploded at a second shot point along said line. After the.second shot has been recorded, the. same operations are. repeated at athird and any desired number of further points, a continuous profilingof underground formations being thus effected along a survey lineextending any desired number of feet or miles.

As mentioned hereinabove, the type of record obtained at the recordingunit may be either of the variable-amplitude type, wherein the vibrationof the movable element of the detector in response to ground waves isrepresented by a line having a variable amplitude of oscillation, or ofthe variable area type, wherein the areas to the two sides of thevariable amplitude oscillating line appear in contrasting, usually blackand White, colors.

Should records of the variable amplitude type be obtained in the field,they can be readily converted to contrasting variable-area records byany suitable method, such for examvpie as applying by hand black ink tothe record to one side of the oscillating line photographically producedthere. However, should it be desired to obtain contrasting variable areaseismic records directly in the field, this can be readily achieved bymeans of any suitable method and equipment such, for example, asdescribed in my above-mentioned patent application Serial No. 217,541,which method, forming no part of the present invention, will not befurther described here.

In any case, records of the variable amplitude, variable area, variabledensity or for that matter, of any other desiredtype, can all be used assuitable material in prac ticing the method of the present invention, aswill appear from the description hereinbelow.

' Referring to the drawings, FIG. 1 illustrates a composite seismogramcomprising a plurality of variable area records obtained along aprofiling line extending from south to north, as generally indicated bythe letters S-N at the top of the record. The several multi-traceseismograms, obtained as outlined above by exploding successive chargesat shot points 1, 2, 3, 4, and 6, arranged side by side in properorderand photographically reduced to a suitable size to form the single printor photograph of FIG. 1. It will be seen that the area of FIG. 1actually gives a cross-section view of the ground along a vertical planepassing through the profiling line SN. The various formation layers, andthe interfaces therebetween, where the seismic waves traveling from theshot points are partially reflected and partially refracted, are shownin the composite seismogram of FIG. 1 as oscillations appearing alongapproximately horizontal lines across the successive traces forming saidseismogram.

However, although the composite seismogram of FIG. 1 permits, to acertain degree, to visualize an inspection the underground conditions orstratification along the profiling line, such picture lacks theaccuracy, continuity and clarity, required for instant visualization ofunderground conditions. This is due to several causes and may becorrected as follows in accordance with the present invention.

First, the dimensions of the composite seismogram in the horizontaldirection should be made to a uniform scale, and said scale shouldpreferably be reduced or compressed as compared with the vertical scale.As stated above, the composite seismogram is formed by arranging side byside a plurality of individual seismograrns obtained from a seriesseismometer spreads disposed along a profiling line. These individualseismograms, being made by standard equipment on standard photographicpaper, are necessarily of the same width, whereas the actual seismometerspreads to which they correspond may differ from each otherlongitudinally (along line S-N) by as much as 2000 feet. Thus, forexample, if the distance between shot points 2 and 3 is 3000 feet, whilethat between shot points 3 and 4 is 2000 feet, the spacing betweenpoints 2 and 3 in FIG. 1 should be equal to one and a half times thespacing between points 3 and 4 instead of being equal thereto.

Second, the vertical scale of the composite seismogram must be correctedfor two principal errors; the increase of seismic wave travel velocitywith increasing depth, and the effect of the weathered layer. It will berealized that the vertical scale of the composite seismogram of FIG. 1is in fact a time scale, wherein equal vertical linear spacingscorrespond to equal times or periods of seismic wave travel rather thanto equal actual vertical distances traveled through during said periods.Since the speed of seismic wave travel is considerably greater atgreater depths, the use of a vertical time scale results in a distortionwhich it is one of the objects of the present invention to eliminate byautomatically converting said time scale to a proper distance or depthscale. Likewise, the wave travel velocity in the upper or weatheredlayer being considerably less than in consolidated layers, the actualthickness of said weathered layer at the location of each seismometerspread affects the total time necessary for the reflections to reach theseismometers, and thus may bring into the composite seismogram anotherinaccuracy which it is likewise the object of this invention toeliminate.

FIG. 2 shows a plan view of an arrangement used in carrying out themethod of the present invention. This comprises a horizontal table 12having a narrow transverse slot 13. If desired, table 12 may be made oftwo portions 15 and 17 movable with regard to each other. By telescopingportions 15 and 17, the widths of the slot 13 may be varied betweenlimits such as .1 and .001 of an inch. A source oflight, located underthe table 12 and therefore not shown in FIG. 2, projects light beamsvertically upwards through the slot 13, which serves thus as theobjective lens of the photographic system of the present invention.

Rotatably supported on the table 12 on bearings 16 are two parallelhorizontal leads screws 18 and 19 driven by a motor 21 through a geartrain generally denoted by the numeral 23. The lead screws 18 and 19 areprovided with clutches 27, 28 and 29 by means of which screws 19 can bedisconnected from motor 21 and connected for operation to motor 30, aswill appear hereinbelow.

Mounted for axial motion along the lead screw 18 is a traveling nut 33,supporting a bracket 35 provided with locking means 37 for clampingtherein a film .or sheet, such as a sheet of sensitized photographicpaper 38.

Mounted for axial motion along the lead screw 19 is a traveling nut 39supporting a carriage 40. Mounted in carriage 40 at right angles to leadscrew 19 are two smaller lead screws 41 and 43 actuated for axialmovement at right angles to the axis of lead screw 19 by means ofrotation through driven gears 45 and 47 and a handoperated driver gear49. The movable lead screws 41 and 43 carry attached thereto a bracket51 provided with locking means 53 for clamping therein a sheet, such forexample as a seismogram 5B of the type shown in FIG. 1. Any suitablegear train whereby the speed of one of the lead screws may be variedwith regard to the other may be used for the purposes of this invention,and the gear train 23 illustrated in FIG. 2 is therefore shown merely byway of example. It will be readily seen from the drawing that theconstant-speed motor 21 drives the lead screw 18 through the gears 52and 54, sleeve 55, gears 57 and 59 and bevel gears 61, gears 54 and 57being fixedly mounted on and rotating with the sleeve 55, and gears 59and 61 being fixedly mounted on and rotating with shaft 65. At the sametime, the lead screw 19 is driven by the motor 21 through gears 52 and54, 57 and 59, 67 and 69, shaft 70 and bevel gears 71, the shaft 76,having the gear 69 fixedly attached thereto, passing slidably throughthe sleeve 55 and gears 54 and 57. Gears 67 and 69 are interchangeablegears, so that by selecting a proper gear ratio, the lead screw 19 maybe given any desired speed ratio with regard to the lead screw 18: forexample, speed ratios of from 1:1 to 1:12 may be readily used.

It is understood that in operating the apparatus of FIG. 2 as describedabove the clutch 28 is engaged, and the clutches 27 and 29 disengaged.Should it be desired not only to run the lead screw 19 at a speeddifferent from that of lead screw 18, but also to run it at a variablespeed while retaining the speed of the lead screw 18 constant, this maybe achieved by disengaging the clutch 28 and engaging the clutches 27and 29. It will be seen that in such case, the constant speed motor 21will continue to drive the lead screw 18 at a constant speed and willalso drive, through the clutch 27, shaft and sprockets 77 and 79,connected by a chain 8-1, a horizontal lead screw 83, parallel to leadscrews 18 and 19 and suitably supported on the table 12 between bearings82, while the lead screw 19 will be driven, through clutch 29, a shaft(supported between bearings 87 bevel gears 89 and power shaft 91, by anelectric motor 30, which may be either a variable speed motor having itsspeed controlled electrically in a fashion well known in the art, or aconstant speed motor coupled to the shaft 91 through a vari-,

able speed gear box, whereby the rotational speed of shaft 91, andtherefore of the lead screw 19, can be varied mechanically by means of acontrol knob 95 and rod 97.

Mounted for axial motion along the lead screw 83 are traveling nuts 101and 103. Horizontal bars 105 and 197, each having one end afiixed to oneof said nuts and the other end supported on a rail 109 for motiontherealong, serve to support a carriage platform 1.10 carrying atelescope or other sighting device 112. The platform 110,

which is movable with traveling nuts 101 and 103 axially of the leadscrew 83, is alsomovable in a direction perpendicular thereto along bars105 and 107' by means such as a lead screw 113, a split nut 115 attachedto the platform 110, and meshing bevel gears 117, one of which isattached to the lead screw 113 and the other splined to the shaft 85.for rotation with said shaft and axial motion therealong. It will beseen that with the arrangement described, the platform 110 may be madeto move axially of the lead screw 83 by the constant speed motor 21 atthe same speed as the bracket 35 along lead screw 18, while at the. sametime being moved in a direction perpendicular thereto by the variablespeed motor 30 at theparticular speed used at any given moment to movethe bracket 51 alongv the lead screw 19.

In operating the system of FIG. 2, a transparent negative of a.composite seismogram 50, which may be of the variable density, variableamplitude or variable area type, such for example as shown in FIG. 1, isclamped to the bracket 51 by means of the locking screw 53, while apiece of sensitized paper or film is clamped to the bracket 35 by meansof the locking screw 37, suitable precautions being taken againstexposure to light.

A desired speed ratio between the lead screws 18 and 19 is then providedby selecting gears 67 and 69 having the desired tooth ratio. Thus, forexample, if it is desired to reduce the horizontal scale of theseismogram of FIG. 1 by half, the lead screw 19 is given twice the speedof lead screw 18 by selecting a gear 67 having a. tooth ratio of 2:1with regard to gear 69.

If, during the process, it becomes desirable to change the. ratio of thespacings between the stations 1, 2, 3, etc, this can be readily achievedby stopping, at, appropriate moments, the apparatus, replacing the gears67 and 69 previously used by other gears having the desired tooth ratio,and resuming the operations. At the same time, means are provided forand measures are taken to effect the weathered layer correction whenmaking the seismogram forming the next stage of development of theseismogram of FIG. 1 according to the present method.

A base 111 is provided on the table 12 carrying a hinged support 118,rotatable about the vertical axis of said base. A bracket arm 114 isattached to the support 118, being rotatable about the horizontal axisof said support. A telescope or other suitable sighting device 116,mounted in a universal joint in a normally vertical position at the endof the arm 114, can thus be brought to bear on substantially any desiredpoint of the seismogram 50 as it. travels along the lead screw 19.

The seismogram 50, which is that shown in FIG. 1, is provided with acorrection line 120, which is marked thereon, in any desired manner wellknown to Seismologists, from information available to them from varioussources about the distribution and the thickness of the weathered layerin the region under exploration and particularly along the linedesignated herein as SN.

Thus, as the seismogram 50 and the sensitized paper 38 advance to theright at their respective speeds over the lighted slot 13, the operatorbrings the vertical telescope 116 to bear on the line 120, and causessaid line to remain under the cross-hair of the telescope by operatingthe wheel 49 so as to move the bracket 51, carrying the seismogram 50,at right angles to its motion along the lead screw 19'. As a result, theseismogram 50 is displaced with regard to the sensitized paper 38, andthe weathered layer correction. is. automatically brought into the nextrecord.

It will be seen that this new record, which is shown in FIG. 3, differsfrom that of FIG. 1 in that its horizontal scale is reduced to afraction of that of FIG. 1, and in that it has been corrected for theweathered layer. Thus, it will'be seen that the top border of theseismogram, appearing as a straight black line under the numerals 1, 2,3, 4, 5; 6 in FIG. 1, appears in FIG. 3 as a broken line, whereas theweathered layer correction line 120, appearing as a broken line in FIG.1, appears as asubstantially straight line in FIG. 3. In this manner,discrepancies in thetime of arrival of reflections due to the effect ofthe weathered layer at the locations of the successive shots areeliminated from the seismogram of FIG. 3.

The next step in the present method, after obtaining the seismogram ofFIG. 3,, is to correct it for vertical scale distortion.

For this purpose, the negative of the seismogram ofv FIG. 3 is clampedin the bracket 51, but in a position at right angles to that in whichthe seismogram of FIG. 1 was held previously: thatis, in the positionshown inthe diagram of FIG. 4, flue line SN ofthe seismogram being nowdisposed at right angles to the direction of travel of said seismogram.

The clutch 28 is atv this time disengaged, and the clutches 27 and 29engaged, so that the lead screw 19 is driven by the variable speed motor30 as described before, while the lead screw 83 is driven by theconstant speed motor 21 through sprockets 77 and 79 and chain 81.

To correct the distortion of the vertical scale. of the seismograms ofFIGS. 1 and 3, use is made. of a graph such as shown in FIG. 5, whereinthe depth-time of travel curve 125 indicates the rate of gradualincrease of seismic velocities with depth. Curve 125 is plotted frominformation available to seismologists regarding the, location undersurvey from sources such as special vertical velocity measurements inwells, data from previous seismic surveys, etc.

The graph. of FIG. 5 is positioned on the table 12 under the carriageand the cross-hair of the sighting device 112 is brought to bear on thecurve 125. The constant speed motor 21 is started, the variable speedmotor 30 being started at the same time and at such speed that thetraveling nuts 33 and 34 move along the lead screws 18 and 19,respectively, at the same speed. The constantspeed rotation of the leadscrew 18 is transmitted, through chain 81, to the lead screw 83. As thetraveling nuts 101. and 103, together with the carriage 91 supported onlead screws 88 and 89, begin to move in the same direction and at thesame speed as the traveling nuts 33 and 39, the operator maintains thecross-hair of sighting device 93. on the curve by changing the speed ofthe power shaft 91 by a suitable manipulation of the control knob 95,thereby changing the ratio between the speed of the platform 110 axiallyof the lead screw 83 and its speed at right angles thereto. Since achange in the speed of the power in the position shown in FIG. 4) beginalso to travel at a different rate than the clamp 35 and the sensitizedpaper carried thereby, with the result that the seismogram obtained inthis operation, shown in FIG. 6, has its vertical scale altered as afunction of the curve 125,, that is, has a vertical scale measured intrue units of depth, and not a scale measured in units of time. Asstated above, the time scale is incorrect since seismic velocities, ordistances traveled through per unit time, are not constant, but increasewith depth. The final seismogram shown in FIG. 6, gives therefore a muchclearer and more correct picture of the true geometry of undergroundlayers than do FIGS. 1 or 3 showing the initial and the intermediatestages of the seismograms of the present method.

It will be understood that FIG. 2 illustrates only one embodiment ofapparatus suitable to carry out the present method, and, that saidapparatus may be modified in vari ous respects without departing fromthe spirit of the present invention.

A modified and improved embodiment of the apparatus of the presentinvention is shown in FIG. 7, wherein elements identical or similar instructure or function to those of FIG. 2 are denoted by the samenumerals followed by the letter a.

In the embodiment of FIG. 7, the constant speedmotor 21a drives, througha gear box 23a and a clutch 282., a lead screw 18a. It likewise drives,through a clutch 27a,

splined shaft 85a, meshing bevel gears 117a and a lead screw 113a, acarriage or platform 110a moving on supporting rods 151 and carrying asighting device 112a scanning the depth-time curve 125a. The motor 21aalso drives, through a shaft 70a, gear box 71a, and second lead screw19a, a carriage or platform 40a. A bracket 51a is attached to theplatform 40a and moves with said platform longitudinally of the leadscrew 19, While a motion perpendicular thereto may be imparted to saidbracket by operating a knob 49a to rotate a splined shaft 150, bevelgears 156 and a lead screw 41a.

A variable speed motor 30a (or a constant speed motor having a variablespeed changer 93a) is likewise connectable to drive the lead screw 18aby engaging clutch 29a, clutch 28a being at that time disengaged.

. The operation of the system of FIG. 7 will be clear from the abovedescription of the system, said operation being furthermore similar tothat of the system of FIG. 5.

Thus, when adjusting the horizontal scale of the seismograms, clutches27a and 29a and the variable speed motor 3021 are disconnected. Thenegative (or original transparent seismogram) is clamped in the bracket5121, while a photo-sensitized sheet is clamped in the bracket 35a. Theshafts 18a and 19a are then run at constant different speeds by themotor 21a through the gear box 23a, as already explained with regard toFIG. 2, changes of speed ratios being effected, if desired, by changingthe gear ratios in the box 71a at suitable intervals, and the weatheringcorrection being applied by manipulating the knob 49a.

When adjusting or converting the vertical scale to a true depth ordistance scale from a time scale, the clutch 28a is disengaged andclutches 27a and 29a engaged. The negative (or original transparentseismogram) is rotated through 90 degrees to its former position and isclamped to the bracket 35a, which is run axially of the lead screw 18aby the variable speed motor 30a, and at right angles thereto by theconstant speed motor 21a through the spline shaft 85a, the operatorscanning the time-depth curve 125a and maintaining the sighting device116a thereon by regulating the speed of the shaft 1821 by manipulatingthe knob 95a. The photo-sensitized sheet is at this time clamped to thebracket 51a, which is run by the constant-speed motor 21a. It isunderstood that although the carriage 110a has been shown for simplicityas moving in a plane parallel to base 12a, it may sometimes be foundmore convenient to arrange it in a plane vertical thereto.

It will be appreciated that the apparatus of FIG. 7, being more flexibleand compact than that of FIG. 2, and elimi nating certain of theelements thereof, such as the third lead screw 83 without the loss ofits function, forms a preferred embodiment of the present invention.

I claim as my invention:

1. Apparatus for forming seismograms comprising a base, at least twotrack means parallel to each other supported on said base, carriagemeans mounted on each of said track means, prime mover means gearedthereto for moving said carriage means longitudinally of said trackmeans, clamping means carried by two of said carriage means, one of saidclamping means being adapted to hold a seismograrn sheet said sheethaving superimposed thereon a plotted graph of weathered layer depthvariations, and the other being adapted to hold a photosensitized sheet,said sheets being held in adjacent planes parallel to each other, a slotin said base extending across the path traversed by said sheets duringthe motion of said carriage means, means for illuminating said sheetsthrough said slot, a sighting device supported on said base and controlmeans for maintaining said sighting device trained on said plotted graphduring the motion of the carriage means, said control means beinggearedto one of said carriage means to move said carriage means at rightangles to its longitudinal motion upon a resetting of said controlmeans.

2. Apparatus for forming seismograms comprising a base, at least twotrack means parallel to each other supported on said base, carriagemeans mounted on each of said track means for longitudinal motionthereon, a constant speed motor, a variable speed motor, clutch meansselectively connecting one of the carriage means to either of said twomotors, transmission means connecting another of the carriage means tothe constant speed motor a graph of the variations in the speed ofseismic waves with a depth aflixed to said base, a sighting devicemovably supported on one of the carriage means, means actuated by theconstant speed motor for moving said sighting device parallel to saidtrack means, means actuated by the variable speed motor for moving saidsighting device at right angles to said track means, clamping meanscarried by two of said carriage means, one of said clamping means beingadapted to hold a seismogram sheet and the other being adapted to hold aphoto-sensitized sheet, said sheets being held in adjacent planesparallel to each other, a slot in said base extending between said trackmeans across the path traversed by said sheets during the motion of saidcarriage means, means for illuminating said sheets through said slot,and speed control means connected to the variable speed motor formaintaining said sighting device trained onsaid graph by varying thespeed of said variable speed motor when said clutch means are engaged todrive the carriage means of the photo-sensitized sheet by the constantspeed motor and the carriage means of the sighting device by thevariable speed motor.

3. Apparatus for forming composite seismograms, said apparatuscomprising a base, track means arranged on said base, carriage meanseach mounted on one of said track means, prime mover means gearedthereto for moving said carriage means longitudinally of said trackmeans, a seismogram sheet clamped to one of said carriage means, aphoto-sensitized sheet clamped to a second carriage means, said sheetsbeing held in adjacent planes parallel to each other, a slot in saidbase across the path of motion of said carriage means, means forilluminating said sheets through said slot, two graphs each plotting avariable seismic property of the ground, one of said graphs beingcarried by the base and the other by one of the carriage means, twosighting devices for scanning said graphs, one of said devices beingattached to one of the carriage means and the other to the base, firstcontrol means for keeping one of said sighting devices trained on one ofsaid graphs during the motion of the carriage I means, said firstcontrol means being connected to one of the carriage means to displacesaid carriage means with regard to the other carriage means transverselyto its longitudinal motion by an amount proportional to the amount ofadjustment of said control means required to keep said sighting devicetrained on its graph, and second control means for keeping the secondsighting device trained on the other graph during the motion of thecarriage means, said second control means being connected to said primemover means for varying the speed of the relative longitudinal motion ofsaid first and second carriage means by an amount proportional to theamount of adjustment of said second control means required to keep saidsecond sighting device trained on its graph.

4. Apparatus for forming composite seismograms, said apparatuscomprising a base, carriage means mounted for motion on said base, primemover means geared thereto for moving said carriage means, means forclamping a seismogram sheet to one of said carriage'means and aphoto-sensitized sheet to another carriage means, said sheets beingpositioned adjacent to each other, light source means for'illuminatingsaid sheets substantially in a single plane perpendicular thereto, graphmeans showing a seismic properly of the ground, sighting means forscanning said graph means, one of said means being affixed to a carriagemeans and the other to the base, and control means for keeping saidsighting means trained on said graph means during the motion of saidcarriage means, said control means being linked to said carriage meansfor controlling the motion of said carriage means with regard to eachother and to the base proportionally to the adjustments of said controlmeans required to keep said sighting means trained on said graph means.

5 Means to reproduce a seismic trace recorded in increments of time to areproduction in increments of depth, including a holder for a recordshowing seismic events in. equal time intervals, a scanner to traverse arecord in said holder, a recorder of events scanned by said scanner,drive means imparting relative travel between said holder and saidscanner and drive means imparting relative travel between said scannerand said recorder at a rate different from the relative travel rateimparted by the first mentioned drive means, the diflerence in ratesbeing according to a predetermined pattern dictated by known velocitychange applicable to the particular record.

References Cited in the file of this patent or the original patentUNITED STATES PATENTS Williams Nov. 7, Lotka Mar. 21, ,Hirsch et a1.Feb. 9, Kingsbury May 2, Crudo Oct. 22, Johnson Feb. 14, Silverman Mar.17, Palmer May 4, Hawkins May 29, Snyder Nov. 11, Mertin June 7, WebsterJune 14,

FOREIGN PATENTS Great Britain Oct. 1, France Oct. 15, Great Britain June28,

